The 2004 Venus Transit

Click on the C2 or C3 images below for full-resolution images, or on
the EIT subfield images for an MPEG of all EIT subfield exposures
for the Venus transit.
Mercury enters from the right at the end of the C3 movie.

On June 8, 2004 we had the opportunity to experience a very rare
celestial phenomenon. So rare, in fact, that no living person has ever
observed it before, since the last transit of Venus happened over 120
years ago, in 1882. We will get another chance again, however, in
2012.

As seen from Earth the planet Venus was visible in front of the Sun
for more than 6 hours. From SOHO's perspective, however, 1.5 million
kilometres from Earth and slighly off the Sun-Earth axis, the planet
Venus did not pass in front of the Sun but glided slowly just beneath
the solar disk as shown in the illustration above. However, it was
visible against the emission from the diffuse corona. Thus, scientists
will be able to take advantage of this Venus transit to improve the
quality of data gathered by SOHO.

The difficulty in obtaining accurate data from coronal measurements is
caused by the amount of light coming from the solar disk that bounces
around inside the instruments. This scattered light is also referred
to by scientists as stray light.

When a planet passes in front of the corona it blocks all of the
coronal light coming directly from behind. Whatever light that falls
inside the shadow image is scattered light from inside the
instrument. Distinguishing between light from the solar disk and that
from the corona will allow more refined measurements of the corona.
The fiducial "black spot" formed by a transiting planet is also very
useful for modelling other optical properties of scientific instruments.

As the planet was making its approach towards the Sun, it came
within the range of several instruments that scrutinized it,
including some attempting to detect thermal emissions from the
planet itself.

The transit was be closely watched by several instruments on board
SOHO: LASCO, UVCS, SUMER, EIT, and CDS. Venus was
visible in the LASCO C3 field between June 3 & 13, in LASCO C2
between June 7 & 9, and in EIT between 8:21 UT and 19:05 UT on
June 8.

TRACE images and movies

The TRACE spacecraft is in orbit around the Earth, so they had
essentially the same perspective (and timing!) as ground based
observers. TRACE images and movies of the transit are available on this
page